1. Field of the Invention
This invention is directed to a unit that dispenses a granular material from a hopper to a granular material storage vessel such as a vessel into which pellets or plastic regrind material is loaded before that material is utilized in an injection molding machine. The unit precisely meters the amount of granular material released from the hopper without the use of a conveyor screw.
2. Description of the Prior Art
Conventionally, granular material, which is intended to be blended with virgin plastic, is dispensed from a hopper to a material storage vessel through conveyor screws which precisely meter the amount of granular material fed from the hopper to the storage vessel. Recently, various pneumatic units have been developed which can also control the transport of powdery or granular material by means of a relative suction and pressure flow rate. Representative of such pneumatic units are German Patent 3,803,012 and British Patent Specification 689,680 which show pneumatic conveyers where a hopper drops a particulate substance into a pipe into which compressed air is injected to move the particulate along. In addition, U.S. Pat. Nos. 3,237,805 and 3,512,841 each disclose method and apparatus for conveying particulate material using a gaseous conveying medium. U.S. Pat. No. 5,494,381 shows a bulk material conveying system in which a closed chamber is subjected to a pressurized gas which causes bulk material in the chamber to flow through an outlet and be conveyed through a conveyor.
Serious disadvantages result from use of the prior art apparatus. The conveyor screw can be quite bulky and requires the addition of a mechanical operation for dispensing granular material. Although the various pneumatic units described above eliminate the added mechanical operation of a conveyor screw, they suffer from the inability to precisely meter and control the amount of particulate or granular material being dispensed.
Accordingly, there is a need for a device that will precisely meter and control the amount of granular material released from a hopper without the use of a mechanical conveyor screw.